T-cell immunoglobulin and mucin-domain containing-3 (TIM3), also known as hepatitis A virus cellular receptor 2 (HAVCR2), is a type-I transmembrane protein that functions as a key regulator of immune responses. TIM3 was initially identified on activated IFN-γ producing T cells (e.g., type 1 helper CD4+ T cells and cytotoxic CD8+ T cells) and shown to induce T cell death or exhaustion after binding to galectin-9. More recent studies have indicated that TIM3 expression is also important in regulating the activities of many innate immune cells (e.g., macrophages, monocytes, dendritic cells, mast cells, and natural killer cells). See Han G et al., Front Immunol. 4: 449 (2013).
Like many inhibitory receptors (e.g., PD-1 and CTLA-4), TIM3 expression has been associated with many types of chronic diseases, including cancer. TIM3+ T cells have been detected in patients with advanced melanoma, non-small cell lung cancer, or follicular B-cell non-Hodgkin lymphoma. And the presence of TIM3+ regulatory T cells have been described as an effective indicator of lung cancer progression. See Anderson A C. Cancer Immunol Res. 2: 393-8 (2014).
Several potential ligands for TIM3 have been identified: Galectin-9, HMGB 1, Semaphorin-4A, CEACAM-1, ILT-4 and phosphatidylserine (PtdSer or PS). PS is an important cell membrane component, and is normally localized to the inner leaflet of cell membranes. But as a cell undergoes apoptosis, PS is redistributed and exposed to the outer membrane. This redistribution is also observed in many tumor cell lines. See Riedl S et al., Blochim Blophys Acta. 1808: 2638-2645 (2011). Binding of TIM3 to PS may be critical for phagocytosis and cross-presentation. See Nakayama M et al., Blood. 113: 3821-30 (2009).
Studies have shown a close relationship between TIM3 and the inhibitory receptor PD-1. For example, many tumor-specific T cells express both PD-1 and TIM3, and these T cells have been shown to be more dysfunctional compared to T cells that express only PD-1 or TIM3. See Fourcade J et al., J Exp Med. 207: 2175-2186 (2010).
Accordingly, agents that target TIM3, and methods of using such agents, are highly desirable for designing new cancer immunotherapies and improving traditional cancer immunotherapies.